The baby boy had died aged just two days in 1998 and his family gave consent for a post-mortem examination to take place but they "assumed he had been buried in tact".

She told BBC Radio 4's Today programme: "We had his funeral, we got on with our lives as you have to and 13 years later we have a knock on the door from the Dorset police to inform us that his brain has been retained at Southampton hospital."

Ms Cheevers said she was shocked and "did not know really how to take it".

"We assumed he had been buried intact," she added. "We had absolutely no idea that they had kept his brain."

Police told her that Rhys' brain had been kept in storage untouched but could not tell her why.

Ms Cheevers said they have decided to donate his brain to hospital research after being told the other two options were to have it destroyed or buried with his body.

"I didn't want another funeral. I've got other children now. It's a difficult thing to talk about and I didn't want to have to explain to my young children why we had to have a funeral. And, I didn't really want him dug up to have his brain put with him. I just don't like the thought of having a child dug up after they have been buried for 13 years."

It comes after a BBC investigation found body parts from nearly 90 children were kept by police, often without informing parents. Last year a national audit found police forces had kept almost 500 body parts dating back around 50 years.